Big drop in VO2Max during one workout

     With hard training I gradually worked my way up to VO2Max 59 over the long term. Only did one alpine run yesterday with over 600m of elevation gain. After the workout, which lasted about 1,5 hours and was with a chest strap (no unrealistic heart rate deviations), the VO2Max dropped from 59 to 55.

     That seems very unrealistic to me. Has anyone had a similar experience? Will the VO2Max value quickly return to its original value?

     Thanks for the advice!